1. Field of the Invention
The object of this invention is a method and a device for evaluating a parameter relative to the movement of an object from images.
2. Description of the Prior Art
From document U.S. Pat. No. 4,495,589 we know a method for determining the speed of an airplane, in which at time t1 one takes an aerial photograph of the ground and at time t2 a second aerial photograph, in which one looks for the zone of the photograph taken at time t2 which corresponds to a zone of the photograph taken at time t1. On the basis of these photographs, one determines the distance of shift of the photograph taken at time t2 compared with the photograph taken at time t1. Knowing the difference in time (t2−t1), the altitude of the airplane and the distance of shift in the photographs, one can determine a speed of movement for the airplane.
This method requires a precise analysis of the two photographs to determine the zone where the two photographs intersect. The method according to document U.S. Pat. No. 4,495,589 does not have a great degree of precision when the ground or the objects are close to the camera given the great difference in angle of the two shots of one single zone. Furthermore, the method is unable to give an almost instantaneous speed, constantly evaluated, of the airplane. In this method, one compares parts of images, recorded by a single linear sensor and shot from varying and very different angles.
One knows from document U.S. Pat. No. 4,671,650 an apparatus similar to that represented in U.S. Pat. No. 4,495,589, except that images of radiation energy are taken from the ground by two matrix cameras.
One also knows from document WO96/22537 a system for measuring distance and speed. In this system, two cameras, with parallel lines of vision, are used. One then determines the angular deviation of the object in relation to the lines of vision of the two cameras. To determine a speed, the cameras take pictures at times T1 and T2, and at every time T1 and T2 one determines the position of the target on the basis of the pictures taken respectively at time T1 and time T2. This determining can if necessary be done by determining the sum of the differences of pixel intensity of the lines of vision on the left and those on the right. In this system, pictures are taken at specific times to determine the distance or the speed of an object. There is therefore no question of a development of linear pictures in this method.
The system in this document is adapted to determine speeds of objects moving towards the cameras or away from them in a direction parallel to the vision directions of the cameras. In fact, if the moving object is moving perpendicularly to the vision directions of the cameras, the object will quickly go out of the field of vision of each of the cameras.
In the method according to WO96/22537, one does not compare a development of second linear images with a development of first linear images to determine a first linear image best corresponding to a second linear image and the time difference associated with this correspondence of linear images.